The invention relates generally to a fluid control system and, more particularly, to a hydraulic control system having an independent metering valve arrangement with regeneration capability.
Conventional fluid control systems may include a regeneration capability, which may include the ability to re-direct some of the energized fluid exhausted from a contracting chamber of a double acting hydraulic cylinder to a corresponding expanding chamber. This fluid redirection enhances operational speed over that provided by pump flow only.
One common type of fluid control system with regeneration includes a separate regeneration valve disposed between a main directional control valve and the hydraulic cylinder to provide a quick drop feature for actuators driven in one direction by gravity loads. A problem associated with such a system is that the operator has little or no control over the amount of regenerated fluid recirculated from the contracting chamber to the expanding chamber. Moreover, regeneration takes place only under certain conditions because such regeneration valves are frequently triggered automatically based on system conditions. Additionally, providing a separate regeneration valve is a generally expensive and complex alternative.
In the environment of an independent metering valve arrangement, U.S. Pat. No. 5,960,695 discloses a hydraulic control system comprising an independent metering valve arrangement having regeneration capability during extension of a load based on pressure differences measured across metering valves.
A system that simply and inexpensively provides regeneration capability during retraction of a load is desired. The present invention is directed to solving one or more of the problems set forth above.
According to one aspect of the invention, a fluid control system includes a pump, a tank, an actuating cylinder having a rod end chamber and a head end chamber, and a valve assembly. The valve assembly may include a first valve configured to control fluid communication between the rod end chamber and the tank, a second valve configured to control fluid communication between the rod end chamber and the pump, a third valve configured to control fluid communication between the head end chamber and the pump, a fourth valve configured to control fluid communication between the head end chamber and the tank, and a load hold check valve configured to control fluid communication between the pump and the actuating cylinder. The fluid control system also includes a pressure sensor configured to sense a pressure of fluid at the head end chamber and a controller in communication with the valve assembly and the pressure sensor. The controller may be configured to selectively actuate the valves based on the sensed pressure at the head end chamber and a mode of operation of the control system.
According to another aspect of the invention, in a hydraulic system including a pump, a tank, an actuating cylinder having a rod end chamber and a head end chamber, and a valve assembly, a method for controlling the hydraulic system includes sensing a pressure of fluid at the head end chamber and selectively actuating the valve assembly based on the sensed pressure and a mode of operation of the hydraulic system.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.